The present invention relates to a liquid crystal projector for projecting on a screen with a magnified output image from a personal computer, CD, video, or the like, especially to a structure thereof for preventing leakage of a light from a light source, improving a cooling efficiency of a light source region and reducing an air current noise from a cooling fan.
There has been used a liquid crystal projector in which an optical image signal formed on a light bulb is radiated by a lighting means and projected onto a screen as a magnified image by means of a projector. There have been proposed also a number of light bulbs with utilization of a liquid crystal display element. A known twisted nematic (TN) type of one of liquid crystal display elements comprises a pair of transparent substrates which have transparent electrode film coats and between which a liquid crystal is filled. At a front and a back sides of the liquid crystal display element, two polarizers are disposed, respectively, in such a manner that the polarizers differ in polarizing direction from each other by an angle of 90 degrees. In such liquid crystal display element, a permeated light quantity of an incident light is controlled to display an image information by combining an action of rotating a polarizing face by an electro-optical effect of the liquid crystal and an action of selecting a polarizing component of the polarizers.
A presentation is made using an image display device by disposing a liquid crystal projector in front of listeners (or audience). In this case, light leakage from a light source deteriorates a quality of image or a contrast on a screen, or a light is flashed directly upon eyes of the listeners uncomfortably. Also, heat generated from the light source not only shortens a life of the light source but gives an adverse influence onto components of the liquid crystal projector. To solve the problem, as disclosed in JP-A-64-84290, a louver as a shade is associated with a lamp house or a housing of the light source to intercept a leak light while a cooling air current can pass through openings of the louver.
In detail, a light source consists of a light emitting portion and a reflective mirror which radiates a light emitted from the light source onto an irradiation face as a target. The reflective mirror is subjected to a dichroic treatment so that unnecessary lights like as an extreme infrared light and a ultraviolet light other than a visible light permeated through the reflective mirror without being reflected by the reflective mirror. Because such unnecessary lights exchange heat in a liquid crystal panel, a polarizing plate and other optical components, and influence the components. The dichroric reflective mirror allows not only unnecessary lights but also a visible light to permeate therethrough. The light which is emitted from the light source and permeates through the reflective mirror leaks and causes problems.
On the other hand, regarding the cooling of the light source region, because of a large output, it is designed to obtain an increased cooling effect by providing the cooling fan in the vicinity of the light source. In this case, a cooling air current path needs to be narrowed for the light leakage. Therefore, when the cooling fan is operated, an eddy airflow arises around the louver and a noise is generated when the cooling air current passes through the louver.
In the presentation mentioned above, the output of the light source tends to be increased such that the presentation can be effected in a lighted hall. This causes problems of the overheating of the light source device and the cooling air current noise and amplifys the light leakage problem mentioned above. In the conventional method using the louver, the light leakage and the cooling efficiency contradict each other. In order to intercept the leak light, a dimension of an opening area of the louver needs to be reduced. However, when a passage area of the cooling air current is reduced, the cooling efficiency of the light source device becomes lower and a noise is increased. There has been tried a structural modification of the louver, and proposed a way of overlapping louver fins. However, such known ways are unsatisfactory.